1. Field of the Invention
This invention relates to a polysiloxane having high photopolymerization inducibility with respect to radical-polymerizable monomers. More specifically, this invention relates to a polysiloxane containing a dithiocarbamate group as a photo-functional group.
As is well known in the art, polysiloxanes which are generally called silicone have for their own properties water repellency, lubricating properties, releasability, resistance to thrombus, biocompatibility, chemical resistance, water resistance, weather resistance, electrical insulating properties, heat resistance, cold resistance and so on (see Isao NAKAJIMA and Kinji ARIGA "Silicon Resins", Nikkan Kogyo Shinbunsha (1960)). On the other hand, great expectations are placed on such polysiloxanes for use in fields where photo-reactions such as photo-curing and photopolymerization are utilized, for instance, in the fields of photo-resists, photoflexographic inks, photo-curing inks, photo-curing paints, photo-curing adhesives, photo-curing binders, photo-curing sealants, medical materials and dental materials.
The present invention provides a polysiloxane photopolymerization initiato r having high photopolymerization inducibility with respect to radical-polymerizable monomers.
2. Background Art
Heretofore, the following techniques have been proposed for the application of polysiloxanes to photopolymerization systems.
(1) Polysiloxanes are merely mechanically mixed with radical-polymerizable monomers and photo-initiators to carry out photopolymerization, thereby obtaining polymer compositions.
(2) Polysiloxane macro-monomers are mechanically mixed with radical-polymerizable monomers and photoinitiators to carry out photopolymerization, thereby obtaining graft polymers (see, e.g., Japanese Patent Laid-Open (Kokai) Publication No. 61-19606).
A problem with the above technique (1) is that since the product is only a mixture of polysiloxanes with other polymers, macro-phase separation, bleeding-out and interface separation and other phenomena will inevitably occur between the two polymers and the product will hardly possess or retain the desired properties of polysiloxanes per se.
With the above technique (2), on the other hand, it is possibly expected to prevent such phenomena as mentioned in (1), for instance, macro-phase separation, bleeding-out and interface separation, from taking place due to polysiloxanes being chemically bonded to the polymers formed by photopolymerization. However, a problem with this is again the failure of the possession of the desired properties of polysiloxanes per se due to the fact that the mobility of polysiloxane macro-monomers is in fact so low and the life of the formed polymer radicals is so short that the probability of contact of both materials is considerably small, thus allowing much unreacted matter to remain in the product.